Okay just to clarify. From my Binance account, I sent it directly to his Binance account & not a non-custodial wallet. Then in his Binance account, we used the "Convert" option to other crypto so we converted USDT to Bitcoin. Hope this clarifies a lot.
Well, where you took the first step, your dad will take the second one. However, I agree that it would be a better option if you sent him BTC directly to his wallet. Somehow, I have a feeling that the first contact with cryptocurrencies through a centralized exchange is the wrong approach. The whole point of cryptocurrencies is decentralization and being your own bank. You would also save on some fees.
Of course, it would help if he also explain why is he betting on bitcoin and what's the factors that make him decided to invest in it, and if it's because of you.
I did opened up to him about moving it to non-custodial Bitcoin wallet if he wants to store and not trade, but he chose to stick with Binance. So it's his decision anyways, so I should respect that. He is illiterate in crypto as a baby boomer & senior citizen.
He's not really open minded though and has a lot of pride. It's just his own instincts that he only wants to buy Bitcoin.
You need to be persistent and introduce him to all the advantages of a properly secured personal wallet, and all the disadvantages and risks associated with keeping money in custodial wallets. I'm sure he will understand if he values your advice. I would hate to see his first experience end up being negative in case of any issues with holding money at the exchange.